The Mesozoic Era: Plants & Animals

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  • 0:01 Definition of Mesozoic Era
  • 1:03 Triassic Period
  • 2:46 Jurassic Period
  • 4:03 Cretaceous Period
  • 6:05 Lesson Summary
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Lesson Transcript
Instructor: Jordana LaFantasie

Jordge teaches college Biology, Ecology and Environmental Science. She has a Doctorate degree in Agronomy.

The Mesozoic Era is characterized by the evolution of many species and marked by two major extinction events at the beginning and end. We will investigate major plant and animal groups that emerged during the Mesozoic Era. The lesson is followed by a brief quiz.

Definition of the Mesozoic Era

The Mesozoic Era is a geological era that began 252 million years ago with a mass extinction and ended approximately 66 million years ago with another mass extinction called the K-Pg Extinction. 'Mesozoic' means middle animals, signifying a transition in animals between the prior era (the Paleozoic) and the following era (the Cenozoic). There were also major changes in global plant life during the Mesozoic era, especially on land. The Mesozoic Era is divided into three major geological periods, which may be more familiar to us: the Triassic, the Jurassic, and the Cretaceous.

Geologic Timeline: Find the Mesozoic Era in the second eon, the Phanerozoic
Geologic Timeline

The era is generally known as the Age of Dinosaurs, but what other animal groups, and what types of plants existed or evolved during this period of time? Let's explore the plants and animals of each period of the Mesozoic Era.

Triassic Period

First, let's take a look at the Triassic Period, including the survivors and diversification after the Great Mass Extinction.

The Triassic was a major period of transition in animal species, starting with very low diversity after the largest extinction event in Earth's history and recovering to higher diversity over a period of 4 to 6 million years. Dinosaurs appeared and evolved during this period, but continued to diversify and dominate for the remainder of the Mesozoic Era. The first flying vertebrates (backboned animals) evolved during the latter part of the Triassic period.

Turtles, crocodile-like species, and frogs made their first appearances during the Triassic, as well. Sea animals included some survivors of the mass extinction event at the end of the Paleozoic Era including ammonites (much like the modern-day Nautilus), brachiopods, and mollusks (modern-day snails are mollusks), and new reptiles including plesiosaurs and ichthyosaurs.

Artist rendition of a pterosaur, the first flying vertebrates


One other major group evolved during the Triassic: mammals. Mammals began as tiny animals (like a mouse), and did not diversify or become very important until after the end of the Mesozoic Era.

Terrestrial plants, or plants that live on land, were primarily dominated by gymnosperms. Gymnosperm (meaning 'naked seed') groups evolved during the upper Paleozoic (the era prior to the Mesozoic) and included conifers (a familiar conifer would be a pine tree) and cycads (which look like palms and have leaf-like reproductive organs).

Modern-day cycad; these are often used as houseplants and for office decor

Jurassic Period

Next, let's take a look at the Jurassic Period.

During the Jurassic, the climate of most land was tropical and dinosaur species filled most ecological roles, including herbivores and carnivores. Some reached enormous sizes, which is probably an indication of the abundance of vegetation (food for herbivores). It was during this time that the stegosaurs became important, and ammonites were significant predators in the sea.

Stegosaurus skeleton, one of many dinosaurs that became common during the Jurassic Period
Stegosaurus skeleton

Mammals had begun to diversify, but were still very small in dominance and size. Birds made their first appearances (birds evolved from therapod dinosaurs; the first official 'bird' was called Archaeopteryx) and had begun to diversify by the end of the Jurassic period.

Archaeopteryx fossil

Rendition of Archaeopteryx; thought to be the first bird genus

Terrestrial vegetation was still dominated by ferns, cycads, gingkos, and conifers - all gymnosperms. Insect herbivores, especially beetles, diversified during this time to feed on the abundant vegetation.

Gingko fossil leaf
Gingko fossil leaf

Modern Gingko biloba leaf. An ancient species, this tree is used extensively in urban plantings.
Modern Gingko biloba

In the sea, microscopic animals diversified, and the species and abundance of sponges and corals increased, creating reefs. Sharks continued to survive alongside other water-sauropod species, and the first bony fishes evolved.

Cretaceous Period

Finally, let's take a look at the Cretaceous Period.

The Cretaceous Period is mostly known for how it ended. It was the end of the Mesozoic Era and the beginning of the Cenozoic Era, which is the current era. However, this is an important period in diversification of life and the arrangement Earth's continents, and should not be ignored. New species emerged, but instead of being common to all of the continents, some are unique to certain landmasses because continent configurations continued to change due to plate tectonics.

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